Magnetic data storage systems commonly include one or more magnetic recording heads that write and read information to and from a magnetic recording medium, respectively. Variable bit aspect ratio capabilities have been suggested to allow some zones of a magnetic recording medium to have a different target bit aspect ratio (BAR) than other zones. See, for example, U.S. Pat. No. 8,842,503, assigned to the assignee of the present application and incorporated by reference herein. Bit aspect ratio is often expressed as a ratio of the down-track dimension (e.g., length) of a bit with respect to the cross-track dimension (e.g., width) of a bit.
VBAR can be used, for example, to designate different zones on the magnetic recording medium for different purposes, such as for capacity purposes and for performance purposes. Generally, large capacity recording media tend to have smaller bit aspect ratios to accommodate the increased number of storage bits on the media, while higher performance media tend to have larger bit aspect ratios to accommodate access requirements. VBAR can be used to improve functionality of a single magnetic recording medium, for example, when part of the disk drive is needed for performance and another part is needed for capacity. Different zones in different regions of a recording medium can thus have different bit aspects ratios and associated areal density capabilities (ADCs) (measured, for example, in gigabits per square inch (GBPSI)).
In Shingle Magnetic Recording (SMR) technology, two-dimensional VBAR (2D-VBAR) techniques have been suggested to maximize ADC values by varying bit aspect ratios in two dimensions (e.g., BARs linearly along given tracks and BARs based on track pitch). Generally, while one-dimensional VBAR schemes measure one pair of a data density value (e.g., bits per inch (BPI)) and a track density value (e.g., tracks per inch (TPI)) and gives one ADC under one pre-defined condition, two-dimensional VBAR allows measurement of multiple pairs of BPI/TPI values and selects the maximum ADC out of all of the measurements.
A need remains for improved techniques for selecting data density values (e.g., bits per inch picked (BPIP)) and track density values (e.g., tracks per inch picked (TPIP)) in multi-dimensional VBAR systems in order to meet a target capacity. A further need remains for multi-dimensional techniques for selecting data density values and track density values that make use of measurement results collected during 2D-VBAR processing to obtain a correlation between data density values and track density values for various bit error rates (BERs).